The decidualized hamster uterus will be used as an experimental model system. Preliminary results indicate estrogen receptor regulation and function may be impaired in deciduoma as compared to myometrium. Studies are designed to: (1) determine serum steroid (estrogen and progesterone)-receptor (estrogen receptor, and progesterone receptor) relationships during decidualization; (2) evaluate the physicochemical properties of cytosol and nuclear receptors; (3) develop a nuclear acceptor site assay to monitor changes that may occur in deciduomal nuclei; (4) establish conditions for culturing deciduomal cells in vitro so as to evaluate effects of steroids, cyclic nucleotides, prostaglandins, and other factors on cell growth and development; (5) identify specific biochemical endpoints of progesterone action in deciduomal cells, including specific proteins, RNA and DNA synthesis, ornithine decarboxylase, polyamines, cyclic nucleotides, and prostaglandins. These studies will provide information relevant to: a) the treatment of hormone-dependent tumors, and b) the development of new contraceptive techniques.